You said it the slave cylinder was leaking to replace it how can i tell if its bad if its not leaking

Usually when you have a bad clutch slave cylinder you know it right away because since it is a hydraulic part, once a seal inside the slave cylinder gets bad, it will start leaking fluid, at the same time, because the seal is not sealing properly, it will allow air inside the system causing your clutch pedal to feel soft and spongy.
When a clutch pedal feels that way, its an indication of air in the system and when this happens it makes it hard to operate the clutch properly because it engages even with your foot almost all the way to the floor. at times you may not even be able to place your car or truck in gear due to this problem.
A bad clutch master cylinder will have similar symptoms, make sure that you look closely at each one of these items to determine which one is the problem (the one malfunctioning will be the one leaking fluid)
One check you can do on the master cylinder is to depress the clutch pedal while someone watches the brake fluid reservoir level. if the level rises while the clutch pedal is being depressed than the clutch master cylinder is bad and should be rebuilt or replaced.